Yes you can, but does the manuf recommend it? I tend to lean towards the oil specially made for bikes. I like the amsoil and all, and I am sure it would be ok, but, there are some people out there that don't like it. So, I guess it is your call. Hope this helps. 73 sportster94 kawasaki klr 25099 monster 75002 monster S4

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Any good 20/50 motor oil that is wet clutch safe is fine. I like the Valvoline Motorcycle Motor Oil. Just make sure it is wet clutch safe. Like no friction modifiers. You can also use the Mobile 1 synthetic that is safe for wet clutch. Or you can use the Amsoil Synthetic that is safe for wet clutches. Amsoil gives you a longer mileage run on their oil then conventional synthetic.

You engine uses three quarts of 20W50 oil. The primary and transmission share the same oil and it uses about a quart of oil. One the late model Big Twins, you can use H-D's Syn 3 in all areas. Not sure about the Sportster. I've always used the H-D primary/transmission lubricant for Sportsters. If you wish to use any other brand of lubricant, you need to go to their website and check to see what they say use in what area. Some of the other popular lubricants are Amsoil, Royal Purple, Mobil V-Twin, and Red Line.

A Harley Sportster, and their Big Twins for that matter, do not have oil in the crankcase. They are what we call "dry sump" engines in the fact that they carry their oil in a seperate remote oil tank.

On your Sportster, you can use Harley's Syn3 20W50 oil in the oil tank. There are other manufactures that make fine oils suitable for your engine but you'll have to check their websites for their recommendations. Amsoil, Royal Purple, Mobil V-Twin are a few.

On the transmission and primary, I'd use H-D semi-synthetic primary and transmission lubricant. There may be other brands that are available as well.

Your 2005 RK came with H-D Syn3 20W50 synthetic motor oil in the transmission. There are other lubricants available such as Amsoil, Royal Purple, and Mobil. You'll have to go to their websites to find out which ones are compatible with your intended usage.

I don't know what you are referring to when you say "secondary". The best engine oil is the H-D Syn3 20W50 oil. You can use most any oil you want as long as it has the proper API rating. I think Harley requires a "C" rating on their oil for use in diesel engines.

For the "primary" case and transmission, I use H-D Primary lube for Sportsters if I can find it. Harley had changed over to another name for the Sportster oil.

Now, there are several other manufacturers of lubricants that are suitable for use in your Sporty. Manufacturers like Amsoil, Royal Purple, Mobil, and a few others. You'll have to go to their websites to get a list of what to use where.

If the bike is 2005 Harley Davidson XL1200 Sportster, it uses Harley Davidson Syn3 20W50 oil. You can use any good petroleum or synthetic oil of this weight as long as it has a API code rating with CG or better for use in diesel engines. Amsoil makes a good substitute or Mobil V-Twin.